Investigation of thickness dependence of the ferroelectric properties of Pb(Zr0.6Ti0.4)O3 thin-film capacitors

Abstract

The ferroelectric properties of Pt∕Pb(Zr0.6Ti0.4)O3∕Pt∕TiO2∕SiO2∕Si thin-film capacitors with different thicknesses are investigated. According to the literature data, tilting of the hysteresis loops and marked increase of the coercive fields are observed when the thickness of the film is reduced. The degradation of the switching properties is fully reproduced by simulations including nonferroelectric space-charge layers at both ferroelectric/electrode interfaces. Based on the theoretical results, a converse model is constructed from which the overall interface capacitance, the total interface built-in potential, and both dielectric permittivity and polarization of the bulk ferroelectric layer are determined for each film. Remarkably the polarization loop due to the switching domains, calculated for each Pb(Zr,Ti)O3 (PZT) capacitor, exhibited a squarelike shape with coercive fields in agreement with the bulk value. Moreover, a unique set of parameters was found whatever the film thickness. From our results it is concluded that the degradation of the ferroelectric properties of metal-PZT thin-film-metal capacitors, often encountered when their thickness is reduced, probably arises from a mechanism of modulation of density and sign of the space charge at both interfaces.

On the influence of the top and bottom electrodes—A comparative study between Pt and LNO electrodes for PZT thin films

“…Obviously, modification of these properties may be related to interface deterioration. In the framework of stacked-PZT capacitor model in which the ferroelectric bulk layer is sandwiched by two nonferroelectric spacecharge layers [16], we infer that the use of Pt top electrode returns to decrease the interface capacitance and to increase the interface built-in potential. Therefore, it is likely that utilization of LNO, notably at the surface of the film, yields an evident enhancement of interface properties.…”

Effect of film thickness on interface and electric properties of BiFeO3 thin films

“…The thickness of ferroelectric films influences the lattice parameters, strains, leakage current densities, and ferroelectric properties. The effect of reducing thickness of BFO films on ferroelectric behavior was theoretically calculated based on a general Landau free energy function [18]. However, no experimental discussion of the cause of the degenerated ferroelectric behavior of BFO films had been reported.…”

Interface depolarization field as common denominator of fatigue and size effect in Pb(Zr0.54Ti0.46)O3 ferroelectric thin film capacitors

“…In previous investigations devoted to size effects, we apply this criterion on fresh samples of different thicknesses. 24,34 This procedure, achieved by adjusting the amplitude of the applied voltage, amounts to restore a similar inner polarization loop, close to saturation, in the bulk ferroelectric layer of each sample. In fine this simply returns to compensate for the voltage drop across the interface capacitance.…”

“…It was indeed established that the effect of interface charge is cancelled at the moments where the applied voltage reaches its maximum values because they correspond to the moments where the charge change sign. 34 Since fatigue polarisation is typically estimated at constant amplitude of the applied voltage, then a drop of polarization due to the switching domains, hence of D r , is still expected.…”

“…In order to check if fatigue and size effect are governed by the same phenomena, we try now to interpret the hysteresis measurements by referring to this model. According to the original work, 34 the total interface built-in potential V bi due to space charge may be estimated by plotting E c versus 1 / d, where d is the film thickness. The E c fields are external values, i.e., the sum of the internal, or bulk, coercive values relating to the polarization due to the switching domains ͑E fc ͒, and of the static field due to the interface space charge.…”